Part 42 (1/2)

Aside froed, it is sometimes customary to require a chemical analysis of the brick Such an analysis is only necessary as deter the aO and FeO) These fluxes are ordinarily combined into one expression, indicated by the symbol RO This total becomes important only above 02 molecular equivalent as expressed in ceramic empirical formulae, and this limit should not be exceeded[75]

From the nature of fire brick, their value can only be considered fro, what are known as first-grade fire brick may be divided into three classes, suitable for various conditions of operation, as follows:

Class A For stoker-fired furnaces where high overloads are to be expected or where other extreme conditions of service are apt to occur

Class B For ordinary stoker settings where there will be no excessive overloads required from the boiler or any hand-fired furnaces where the rates of driving will be high for such practice

Class C For ordinary hand-fired settings where the presumption is that the boilers will not be overloaded except at rare intervals and for short periods only

Table 61 gives the characteristics of these three classes according to the features deter the quality This table indicates that the hardness of the brick in general increases with the poorer qualities

Provided the hardness is sufficient to enable the brick to withstand its load, additional hardness is a detrie

TABLE 61

APPROXIMATE CLassIFICATION OF FIRE BRICK

________________________________________________________________________ | | | | | | Characteristics | Class A | Class B | Class C | |_____________________|________________|________________|________________| | | | | | | Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees| | Fahrenheit | 3200-3300 | 2900-3200 | 2900-3000 | | | | | | | Compression Pounds | 6500-7500 | 7500-11,000 | 8500-15,000 | | | | | | | Hardness Relative | 1-2 | 2-4 | 4-6 | | | | | | | Size of Nodules | Mediue | | | | | | | | Ratio of Nodules | High | Mediuh | Medium Low | | | | | to Medium | |_____________________|________________|________________|________________|

An approximate determination of the quality of a fire brick may be made from the appearance of a fracture Where such a fracture is open, clean, white and flinty, the brick in all probability is of a good quality If this fracture has the fine uniform texture of bread, the brick is probably poor

In considering the heavy duty of brick in boiler furnaces, experience shows that arches are the only part that ordinarily give trouble These fail fro up of brick This feature is treated below

The tendency of a brick to beco point The limits of allowable plastic te This action occurs on the inner ends of coh velocity at the full furnace teh cold air striking the heated brickwork Failure froe increase in nues are to a great degree eliminated Furthermore, there are a number of brick on the market practically free from such defects and where a new brick is considered, it can be tried out and if the defect exists, can be readily detected and the brick discarded

Failures of arches from the expansive power of brick are also rare, due to the fact that there are a number of brick in which the expansion is ithin the allowable limits and the ease hich such defects may be deterh cheh this cause is found only occasionally in brick containing a high percentage of iron oxide

With the grade of brick selected best suited to the service of the boiler to be set, the other factor affecting the life of the setting is the laying It is probable thatdifficulties arise fro up of brick than froht it is necessary that the masonry work be done most carefully This is particularly true where the boiler is of such a type as to require combustion arches in the furnace

Red brick should be laid in a thoroughly mixed mortar composed of one volume of Portland cement, 3 volumes of unslacked lime and 16 volumes of clear sharp sand Not less than 2 bushels of li up of 1000 brick Each brick should be thoroughly embedded and all joints filled Where red brick and fire brick are both used in the same wall, they should be carried up at the sahly bonded to each other

All fire brick should be dry when used and protected from moisture until used Each brick should be dipped in a thin fire clay wash, ”rubbed and shoved” into place, and tapped with a wooden mallet until it touches the brick next below it It nized that fire clay is not a ce power Its action is that of a filler rather than a binder and no fire-clay wash should be used which has a consistency sufficient to pers should be laid up four courses of headers and one stretcher Furnace center walls should be entirely of fire brick If the center of such walls are built of red brick, they will melt down and cause the failure of the wall as a whole

Fire-brick arches should be constructed of selected brick which are sht and uniform The frames on which such arches are built, called arch centers, should be constructed of batten strips not over 2 inches wide The brick should be laid on these centers in courses, not in rings, each joint being broken with a bond equal to the length of half a brick Each course should be first tried in place dry, and checked with a straight edge to insure a uniform thickness of joint between courses Each brick should be dipped on one side and two edges only and tapped into place with a e brick courses should be used only where necessary to keep the bottoht brick course in even contact with the centers When such contact cannot be exactly secured by the use of wedge brick, the straight brick should lean away from the center of the arch rather than toward it When the arch is approxi should be laid to deter is necessary to secure such a fit, it should be done on the two adjacent courses on the side of the brick away fro course be a true fit from top to bottom, and after it has been dipped and driven it should not extend below the surface of the arch, but preferably should have its lower ledge one-quarter inch above this surface After fitting, the keys should be dipped, replaced loosely, and the whole course driven uniformly into place bythe full length of the keying course Such a driving in of this course should raise the arch as a whole from the center The center should be so constructed that it may be dropped free of the arch when the key course is in place and re burned out

[Illustration: A Typical Steel Casing for a Babcock & Wilcox Boiler Built by The Babcock & Wilcox Co]

Care of Brickwork--Before a boiler is placed in service, it is essential that the brickwork setting be thoroughly and properly dried, or otherwise the setting will invariably crack The bestsuch a process is to block open the boiler damper and the ashpit doors as soon as the brickwork is completed and in this wayIf possible, such preli should be continued for several days before any fire is placed in the furnace When ready for the drying out fire, wood should be used at the start in a light fire which radually built up as the walls becohly heated, coal may be fired and the boiler placed in service

As already stated, the life of a boiler setting is dependent to a large extent upon theinto its construction and the care hich such material is laid A third and equally iiven to the ood condition after the boiler is placed in operation

This feature is discussed eneral boiler roo with the losses operating against high efficiencies as indicated by the heat balance, it has been shown that a considerable portion of such losses is due to radiation and to air infiltration into the boiler setting These losses have been variously esti upon the condition of the setting and the a dependent upon the size of the boiler used In the hest obtainable plant efficiencies much has been done to reduce such losses by the use of an insulated steel casing covering the brickwork In an average size boiler unit the use of such casing, when properly installed, will reduce radiation losses from one to two per cent, over what can be acco and, in addition, prevent the loss due to the infiltration of air, which may amount to an additional five per cent, as coood order Steel plate, or steel plate backed by asbestos ainst the infiltration of air through the boiler setting, is not as effective fro properly insulated fronesia block and asbestos ive excellent results in elie and in the reduction of radiation losses is clearly illustrated on page 306

Many attempts have been s but up to the present nothing has been found that ive as satisfactory service under severe conditions as properly laid brickwork